Smart cards having thin die

ABSTRACT

Thin semiconductor die, approximately 0.004 to 0.007 inches thick, are positioned substantially on the neutral plane of a smart card, the neutral plane defined as the plane of substantially no mechanical strain during flexure of the smart card, thereby providing smart cards having improved resistance to mechanical flexure, and/or smart cards having improved RF performance.

CROSS-REFERENCE TO RELATED APPLICATION

Related subject matter is disclosed in the co-pending, commonly assignedU.S. patent application of E. Suhir—1, Ser. No. 08/551,241, filed onOct. 31, 1995, entitled “Data Carriers Having An Integrated CircuitUnit”, in the co-pending, commonly-assigned U.S. patent application ofClifton-Flynn-Verdi 4-6-15, Ser. No. 08/558,579, filed on Oct. 31, 1995,entitled, “Smart Card Having a Thin Die”, and in U.S. Pat. No. 5,480,842issued on Jan. 2, 1996 to Clifton, Flynn, and Verdi.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor devices, and moreparticularly to semiconductor die that are used in the manufacture ofsmart cards.

2. Background Art

Existing smart cards may fail when, due to applied mechanical stress,the semiconductor die of the smart card breaks. Mechanical stress isinherent in typical smart card operational environments, such aspoint-of-sale terminals, electronic cash machines, credit card readingdevices, wallets, pockets, and purses. Semiconductor die strength is asignificant factor in determining the overall durability and reliabilityof a smart card. Die thickness affects the ability of a semiconductordie to withstand flexure and applied mechanical force.

In the field of semiconductor fabrication, skilled artisans attempt touse the thickest semiconductor die that will fit within a smart cardpackage. This approach is based upon an assumption that die strength isproportional to die thickness. Since existing smart card packages areapproximately 0.030 inches thick, this dimension places a constraint onthe maximum thickness of the semiconductor die which will fit within thepackage. To this end, note that it is not feasible to use semiconductordie that are about 0.030 inches thick. In addition to the die itself,the space within the smart card package is also occupied by leadterminations, structures that protect the die and/or the leads,labeling, magnetic striping, and discrete circuit components. Therefore,die thickness on the order of 0.011 inches are employed, representingthe maximum die thickness that can easily fit within a smart cardpackage. Semiconductor die thinner than 0.011 inches are typically notused in smart cards, as such die have traditionally been difficult tohandle during the manufacturing process, and the resulting manufacturingexpenses are relatively high. Furthermore, conventional wisdom dictatesthat, as the thickness of a die is decreased, the die becomeincreasingly vulnerable to mechanical failure.

A shortcoming of existing 0.011-inch die is that the die do not providesufficient immunity to mechanical flexure. When such die are used tofabricate smart cards, breakage and card failure may result if the smartcard user bends or flexes the card. Accordingly, flexure is anespecially important physical property to consider for smart cardapplications. In order to improve performance in this area, existingapproaches have focused on strengthening the 0.011-inch die through theoptimization of specific individual design parameters, such as grindingparameters, dicing parameters, and others. As opposed to integratingthese design parameters into a broad-based design solution, typicalapproaches have adopted a piecemeal approach by considering the effectsof only one or two design parameters on flexure resistance. For example,in material systems having high thermal coefficients of expansion,design parameters have been optimized for the purpose of increasing dietolerance to severe thermal transient conditions.

Another shortcoming of existing smart card semiconductor die designs isthat little, if any, consideration is given to RF (radio frequency)performance issues. For example, one presently-available smart cardrequires direct mechanical and electrical contact during use, whereasanother type of smart card uses signals in the extremely-low-frequency(ELF) area of the RF spectrum, in the range of 300 to 20,000 Hz, withexisting industry-standard UART protocols of 2400, 4800, 9600, and/or19,200 band. Existing smart cards do not operate at frequencies abovethe ELF region. Although transponder devices and pagers have beendeveloped for use at higher frequencies, such devices occupy a muchlarger physical volume than is available within the confines of a smartcard. Meanwhile, in relatively recent times, high-speed microprocessorsoperating at speeds of around 100 Mhz have been developed, and radiofrequencies in the 800 and 900-Mhz regions of the frequency spectrum arenow enjoying widespread use.

Consider a two-inch lead used in an existing smart card package. Thislead provides negligible inductive reactance at 1 Khz, on the order of afraction of an ohm. That same lead, used at 500 Mhz, provides aninductive reactance of several hundred ohms, which may severely disruptdesired circuit operations at higher frequencies. Moreover, when anexisting semiconductor dice having a thickness of 0.011 inches is usedto fabricate active semiconductor device, these devices provide electrontransit times on the order of several tenths of microseconds,effectively limiting device operation to frequencies less than about 10Mhz.

Existing field-effect transistors for use in the UHF and microwaveregions of the RF spectrum use die thicknesses in the order of 0.00236inches, so as to provide a relatively short electron transit time. Theseshort electron transit times provide increased high-frequencyperformance. One technique for fabricating these field-effecttransistors is described in U.S. Pat. No. 5,163,728 issued to Miller andentitled, “Tweezer Semiconductor Die Attach Method and Apparatus”.Unfortunately, the methods and systems described in the Miller patentare only practical when used to construct discrete transistor devices.The use of tweezer-based devices to construct smart cards is impracticalbecause it would be much too labor-intensive, time-consuming, andexpensive. What is needed is an improved technique for constructing asmart card that has enhanced RF (radio frequency) properties.

Smart card packages are about 0.030 inches thick, thereby providing apackage that is very similar in dimensions to that of a conventionalcredit card. Note that existing smart card packaging techniques placethe semiconductor die near the surface of the card, due to tightpackaging and interconnect requirements, and also because the thicknessof the die represents a substantial portion of the thickness of theactual smart card package. Therefore, if a user bends a smart card backand forth, the semiconductor die, being situated near the surface of thecard, is subjected to relatively high levels of mechanical stress.

RF coupling, as opposed to direct physical contact, is a moreadvantageous technique for sending and receiving data to and from asmart card, in terms of user convenience and smart card reliability.However, semiconductor die material functions as a lossy dielectric,attenuating RF signals that are incident thereupon, including thesignals that are used to couple data to and from the smart card. Thisattenuation limits the maximum coupling distance between a smart cardand a smart card reader, and also restricts the position in which asmart card must be held relative to a smart card reader/writer, in orderto successfully read and write data from and to the smart card. Theattenuation is substantially proportional to the thickness of thesemiconductor die used to fabricate the smart card, inasmuch as thesmart card packaging material is a nonconductive plastic encapsulantoffering very minimal RF attenuation, and the conductive leads to andfrom the semiconductor die occupy an inconsequential portion of thesmart card package.

SUMMARY OF THE INVENTION

Improved smart card semiconductor die are provided that have a thicknessof approximately 0.004 to 0.007 inches. These die are positioned at ornear the neutral plane (i.e., plane of substantially zero mechanicalstrain during flexure) of a smart card, thereby providing smart cardshaving improved resistance to mechanical flexure and/or enhancedperformance at RF frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art smart card semiconductordie;

FIG. 2 is a cross-sectional view of a thin smart card semiconductor diefabricated in accordance with a first embodiment disclosed herein;

FIG. 3 is a cross-sectional view of a thin smart card semiconductor diefabricated in accordance with a second embodiment disclosed herein;

FIG. 4 is a table comparing various physical parameters of the smartcard semiconductor die shown in FIGS. 1, 2, and 3.

FIG. 5 is a cross-sectional view of the smart card semiconductor die ofFIG. 2 in a state of mechanical flexure; and

FIG. 6 and FIG. 7 are a plan view of a smart card showing representativelocations for various smart card components.

DETAILED DESCRIPTION

Existing die strength improvement techniques have not adequatelyaddressed applications involving mechanical die flexure. In the contextof smart card semiconductor die, during mechanical flexure, themechanical stresses are greatest near the card surface, and are at aminimum value along a neutral plane within the body of the smart card.The neutral plane of the smart card may be defined as the plane of nostrain during mechanical flexure of the smart card. If it is assumedthat the smart card package is of a substantially uniform compositionthroughout, with no internal cavities, this neutral plane is at a depthapproximately equal to half the thickness of the smart card, i.e., the“mid-plane” of the smart card. However, as a practical matter, the smartcard package must contain a cavity for accommodating the semiconductordie. Additionally, stickers, laminates, and/or other types of dressingmaterials may be applied to the surface of the smart card foridentification or ornamentation. These cavities, laminates, and/orstickers may shift the location of the neutral plane to a location thatis not approximately equal to half the thickness of the smart card.However, the location of the neutral plane may be determinedempirically, and/or with resort to mathematical calculations well-knownto those skilled in the art.

Since the mechanical stresses are substantially zero at any point on theneutral plane, it would be desirable to position the semiconductor dieat or near the neutral plane. However, even if an existing 0.011 inchdie is centered along the neutral plane, the sheer thickness of the dieitself results in portions of the die being located in higher stressregions near the surface of the card. Note that the thickness of a smartcard must be limited to about 0.030 inches if the smart card is tophysically resemble a conventional credit card. In order to providephysical space within the 0.030-inch-thick smart card package forelectrical connections to a semiconductor die that is 0.011 inchesthick, the semiconductor die must be mounted relatively close to asurface of the smart card.

It is generally difficult or impossible to situate a conventional0.011-inch-thick semiconductor die on or near the neutral plane (i.e.,within a few thousandths of an inch), even if the location of theneutral plane is shifted from a mid-plane location through the use ofcavities in the smart card package, non-uniform smart card packagecomposition, and/or the application of stickers or laminates to thesmart card package. What is needed is a thinner die, such that theentire die can be situated at or near the neutral plane.

One advantage of using a thin semiconductor dice is that a smart cardhaving enhanced RF performance is provided. For example, when anexisting semiconductor dice having a thickness of 0.011 inches is usedto fabricate active devices for use in a smart card, these activedevices often provide electron transit times on the order of severaltenths of microseconds, effectively limiting device operation tofrequencies less than about 4 MHz. To this end, note that existing RFtransistors for use at VHF and UHF frequencies generally use die muchthinner than 0.011 inches, and typically in the range of 0.004 to 0.007inches. By using a thin dice having a thickness in the range of from0.004 to 0.007 inches in a smart card, relatively short electron transittimes are provided, enabling active device operation in the MF, HF, VHF,UHF, and/or microwave frequency ranges.

Device operation at higher frequencies is advantageous in that a smartcard is no longer limited to using industry-standard UART protocols, thefastest of which operates at 19,200 baud. (Note that other standard UARTprotocols used by existing smart cards operate at 2400 baud and/or 4800baud.) In addition to being adapted for use with these conventional UARTprotocols, the thin smart card semiconductor die disclosed herein arealso adapted for use with faster data transfer protocols and modulationschemes that operate at higher speeds than conventional UART protocols.These faster data transfer protocols and modulation schemes may beassociated with higher-frequency RF carriers above 20 Khz, such as, forexample, in the HV, VHF, UHF, and/or microwave regions of the RFspectrum. Such high-frequency RF carriers may be employed in conjunctionwith known RF modulation schemes as for example, QAM (quadratureamplitude modulation), PCM (pulse-coded modulation), FM (frequencymodulation), SSB (single-sideband modulation), and others.

If a smart card uses RF encoding, as opposed to direct physical contact,for sending and receiving data, the use of a thin semiconductor diceprovides another advantage. As discussed above, semiconductor diematerial functions as a lossy dielectric, attenuating RF signals thatare incident thereupon. Since this attenuation is roughly proportionalto the thickness of the die, the use of a thin die reduces the extent towhich RF signals are attenuated by the smart card. This reducedattenuation, in turn, increases the maximum allowable coupling distancebetween a smart card and a smart card reader/writer, and also increasesthe number of locations in which a smart card can be held relative to asmart card reader/writer, in order to successfully read and write datafrom and to the smart card.

FIG. 1 is a cross-sectional view of a prior art smart card semiconductordie 101 mounted in a conventional smart card package 103. Activedevices, such as transistors and diodes, are fabricated near activesurface 105 of semiconductor die 101. Conventional smart card package103 has a neutral plane which, in the cross-sectional view of FIG. 1, isrepresented by axis a-a′. The neutral plane is defined as the plane ofsubstantially zero mechanical strain during mechanical flexure of thesmart card package 103. The semiconductor die 101 is about 0.010 to0.015 inches thick along axis b-b′, denoted as distance H₂. The activesurface 105 of the die is positioned at a distance H₃ greater than 0.005inches from the smart card neutral plane.

FIG. 2 is a cross-sectional view of a smart card semiconductor die 201fabricated in accordance with a first embodiment disclosed herein.Typically active devices, such as transistors and diodes, are fabricatednear active surface 205 of semiconductor die 201. Smart card package 203has a neutral plane which, in the cross sectional view of FIG. 2, isrepresented by axis c-c′. However, unlike the semiconductor die 101 ofFIG. 1, semiconductor die 201 has a thickness along axis d-d′ of about0.004 inches, represented as H₄. Axis d-d′ may be conceptualized asrunning parallel to the thinnest dimension of semiconductor 201, and/orrunning perpendicular to a plane including semiconductor die 201. Thesemiconductor die active surface 205 is situated at a distance H₅ of0.001 inches or less from the smart card neutral plane, represented asaxis c-c′ in FIG. 2.

Although the semiconductor die 201 of FIG. 2 is very thin compared totypical 0.011-inch die, the use of a thin die is advantageous in smartcard design applications. The configuration of FIG. 2 recognizes thesemiconductor die 201 as a major structural, load bearing, component ofthe smart card. A thin die, such as semiconductor die 201, providesgreater mechanical flexibility relative to a conventional die that isjust barely thin enough to fit within a smart card. For example, thetypical 0.011-inch die used in smart cards will not deflect as far as an0.006-inch die if both die are fabricated to have equivalent yieldstrengths. The term “yield strength” is well understood by those skilledin the art.

FIG. 3 is a cross-sectional view of a thin smart card semiconductor die301 fabricated in accordance with a second embodiment disclosed herein.As in the case of semiconductor die 201 of FIG. 2, active devices, suchas transistors and diodes, are fabricated near active surface 305 ofsemiconductor die 301. Smart card package 303 has a neutral plane which,in the cross sectional view of FIG. 3, is represented by axis e-e′.Unlike the semiconductor die 101 of FIG. 1, semiconductor die 301 has athickness along axis f-f′ of about 0.004 inches, represented as H₈. Thesemiconductor die active surface 305 is situated at a distance H₇ of0.001 inches or less from the smart card neutral plane, represented asaxis e-e′ in FIG. 3. Unlike the semiconductor die 201 of FIG. 2,semiconductor 301 is mounted to smart card package 303 using a physicalstandoff 309. Physical standoff 309 functions as a mechanical spacer,holding the active semiconductor die 301 at a desired spatialrelationship with respect to the neutral axis of the smart card, denotedas e-e′. For example, this desired spatial relationship may be toposition the active surface 305 of semiconductor die 301 as close aspossible to the neutral axis of the smart card. An optional bondingagent may be employed to fasten the physical standoff to thesemiconductor die and/or to the smart card package 303. Virtually anymaterial can be employed for the bonding agent, so long as the materialadheres to semiconductor die 301, and/or to smart card package 303.However, the elastic properties of the bonding agent should also beconsidered. For example, the bonding agent should be relatively elastic,deformable, and flexible, to provide the semiconductor die 301 with somefreedom of motion relative to the smart card package while the smartcard package is being bent. Rubber, epoxies, cyanoacrylate esters(acrylics), and/or other types of materials are suitable for use asbonding agents.

FIG. 4 is a table comparing various physical parameters of the smartcard semiconductor die shown in FIGS. 1, 2, and 3. The design of FIG. 1has a die thickness of 0.015 inches, and the active surface of thesemiconductor die is positioned at a relatively great distance of about0.006 inches from the neutral plane of the smart card. When this smartcard is bent, the active surface of the semiconductor die willexperience relatively great forces due to the relatively great distancebetween the neutral plane and the active surface. By contrast, the smartcard design of FIG. 2 has a die thickness of 0.006 inches, and theactive surface of the semiconductor die is positioned at a relativelyshort distance of 0.0005 inches from the neutral plane of the smartcard. When this smart card is bent, the active surface of thesemiconductor die will experience relatively minimal forces due to therelatively short distance between the neutral plane and the activesurface. Similarly, the smart card structure of FIG. 3 has a diethickness of 0.004 inches and the active surface of the semiconductordie is situated 0.002 inches from the neutral plane of the smart card.

FIG. 5 is a cross-sectional view of a smart card 500 constructed inaccordance with FIG. 3 and in a state of mechanical flexure. Suchmechanical flexure exists, for example, when a user bends the smart card500. One must assume that smart cards will be exposed to flexure duringconditions of ordinary or typical usage. The smart card 500 shown inFIG. 5 has a thickness H₉, an upper surface 502, a lower surface 504, aleft-hand edge 506, and a right-hand edge 508. The smart card is flexed(bent), thus forming an arcuate surface at a radius 593 from a focalpoint 591. In other words, the edges 506, 508 of the smart card arebeing forced together, and the middle of the smart card along axis f-f′is being pushed upwards. This may happen if the smart card 500 isresting on a surface, and someone grasps the card at opposite ends withthumb and fingertips while moving thumb and fingertips closer together,or when smart card 500 is placed in a wallet in the smart card user'srear pocket and the user proceeds to assume a sitting position. A regionof tensile stress 522 is formed above the neutral plane, represented byaxis e-e′ in FIG. 5, and a region of compressive stress 524 is formedbelow axis e-e′. A semiconductor die 301 is incorporated into smart card500, and this die has a thickness of H₉. The strains within smart card500 are shown as vectors 520.

A plan view of the smart card 500 described in FIG. 5 is illustrated inFIG. 6. Referring now to FIG. 6, a smart card 500 is shown, along withrepresentative locations for various smart card components. For example,smart card 500 includes microprocessor 302, chip capacitors 304, and avoltage regulation/data conditioning die 306.

A more detailed cross-sectional view of the smart card 500 of FIG. 5 isshown in FIG. 7. In the example of FIG. 7, semiconductor die 301 is athin semiconductor die having a thickness less than 0.011 inches andpositioned at or near the neutral plane of the smart card package 303.The smart card 500 includes one or more polyvinyl chloride (PVC) labels402, 403 which are affixed to upper and lower surfaces, respectively, ofsmart card 500 with adhesive layers 404, 405, respectively. Adhesivelayer 404 adjoins woven material 408. Woven material 408 is affixed topolyester structural members 410 using an adhesive layer 412. Polyesterstructural members 410 and adhesive layers 412 are configured to form acavity, in which is mounted semiconductor die 301. Die attach epoxy 417and optional mechanical stand-off material is used to mount thesemiconductor die 301 onto a copper pad 419. Die encapsulation material427 is used to protect and insulate the semiconductor die 301, and tomaintain the spacing and positioning of wire bonds 423. Dieencapsulation material 427 should have very high resistivity, i.e. be agood electrical insulator, provide good thermal conductivity to carryheat away from semiconductor die 301, provide a hermetic and watertightseal, adhere well to semiconductor die 301, provide mechanicalflexibility and deformability, and provide non-corrosivity with respectto the semiconductor die 301 and any metallic traces that are connectedto semiconductor die 301. Copper pad 419 is traced onto a polyesterprinted circuit board 426, which may include additional copper pads 421.All or some of these additional copper pads 421 may be electricallyconnected to the semiconductor die 301 via one or more wire bonds 423.Adhesive layer 405 is used to attach PVC label 403 to the underside ofthe printed circuit board 426.

When the smart card 500 is bent, the resulting mechanical strains areshown as vectors 520 in FIG. 5. At a given distance from the neutralplane of the smart card, these strains are lowest in relatively stiffsmart card structural components and greatest in relatively flexiblesmart card structural components. With respect to FIG. 7, strains arelowest in structural components such as semiconductor die 301, andstrains are greater in polyester structural members 410 and adhesivelayers 404 and 405. However, the magnitude of mechanical strain existingin a given smart card component is also dependent upon the positioningof that component relative to the neutral plane of the smart card. Ingeneral, the strains for each component are greatest near the outersurface of the component and at a maximum near polyvinyl chloride (PVC)labels 402 and 403. The strains are zero along axis e-e′, representing atwo-dimensional projection of the neutral plane in FIG. 7. If the smartcard 500 of FIG. 7 is bent as shown in FIG. 5, then the smart cardstructural components above this neutral plane are in tension, and thestructural components below this neutral plane are in compression. Thesemiconductor die 301 is positioned so that the devices (diodes andtransistors) on the die are at or near (within 0.007 inches of) theneutral plane.

In order to mathematically calculate the amount of strain onsemiconductor die 301 when this die is packaged into a smart card 500,and to calculate the location of the neutral plane within the smart card500, the entire smart card structure of FIG. 7 must be considered. Thiscalculation requires the performance of mathematically complexoperations that are best completed using an analysis tool known to thoseskilled in the art as the finite element method. However, to simplifymatters a bit, in practice, the loading on the chip is determined bycard flexure and is dominated by the shape of the card structure. Tosimplify further, when the chip cavity of FIG. 7 is omitted from thecalculation of mechanical strain, the neutral plane, represented by axise-e′, is at a distance H₁₀ from the upper smart card surface, and alsoat a distance of H₁₀ from the lower smart card surface. In other words,the neutral plane is situated halfway between the upper and lower smartcard surfaces, i.e., in the mid-plane of the smart card 500.

Reducing H₁₀ reduces the amount of stress on the smart card die 301.This reduction in H₁₀ is achieved by using as thin a die as ispracticable for semiconductor die 301. Further improvements are achievedby constructing smart card 500 such that the most fragile portion of thesemiconductor die 301 is at or near the neutral plane. This portion istypically the location at which active devices, such as transistors anddiodes, are situated within the semiconductor die 301. Morespecifically, the interface between the conducting (metal-doped) portionof the die and the semiconducting (i.e., N- or P-doped silicon body) ofthe remainder of the die is the most fragile portion of semiconductordie 301. This interface is approximated by the active surface definedabove. Locating this interface at the neutral plane further protects thesemiconductor die 301 from mechanical strain, resulting in a smart card500 with improved reliability. polyvinyl chloride (PVC) labels 402 and403. The strains are

Traditional smart card packaging techniques place the die near thesurface of the card due to stringent packaging and interconnectrequirements. However, according to an embodiment disclosed herein,semiconductor die 301 are situated as close as possible to the neutralplane, e-e′, of smart card 500. In this manner, the effective level ofmechanical stress transmitted to the semiconductor die 301 by the smartcard package 303 during mechanical flexure is substantially reduced. Thesmart card package 303 thus affords extra protection to thesemiconductor die 301 by reducing the mechanical stresses realized uponthe die.

Various techniques may be employed to fabricate the relatively thinsemiconductor die 201 (FIG. 2) and 301 (FIGS. 3, 5, and 7) of theembodiments disclosed herein. However, note that traditionalsemiconductor die fabrication techniques for conventional 0.011-inch diecannot be used to effectively fabricate thin die having a thickness of0.008 inches or less. These existing techniques are designed to maximizethe number of usable 0.011-inch semiconductor die produced during agiven time period. If the die are handled and produced too carefully, itwill take too long to produce the die, and production efficiency willsuffer. On the other hand, if the die are handled and produced tooroughly, more die will be produced, but an undesirable high proportionof these die will be defective and unusable. Therefore, existingtechniques strike a balance between rough handling and careful handling,so that the maximum number of usable 0.011-inch die will be generatedduring a given time interval.

When these existing techniques are applied to fabricate thin die of0.008 inches or less, the thinner die are more fragile during thehandling and fabrication process than conventional 0.011-inch smart cardsemiconductor die. Substantially improved yields of thin semiconductordie may be obtained if special die fabrication techniques are applied tothe semiconductor wafer from which the thin semiconductor die are made.These fabrication techniques include taping the semiconductor wafer withconventional UV dicing tape and then immersing the wafer into an acidbath. The acid bath, which may include nitric acid, hydrofluoric acid,and acetic acid in relative proportions of 7:2:1, provides chemicalstress relief for the semiconductor wafer. Additionally, thesemiconductor wafer may be diced using a dicing saw, soft rubber orplastic die pickup heads, non-piercing ejector pins, and servo orprogrammable dynamic ejector pins to reduce or eliminate die damage.Moreover, the die may be ejected from the dicing tape usingvelocity-controlled or programmable servo-controlled, non-piercingejector pins. Suitable techniques for manufacturing smart cardsemiconductor die are set forth in greater detail in U.S. Pat. No.5,480,842 entitled, “Method for Fabricating Thin, Strong and FlexibleDie for Smart Cards”.

The invention claimed is:
 1. A semiconductor die for use in a smartcard, characterized in that the semiconductor die is less than 0.008between 0.004 and 0.007inches thick.
 2. A semiconductor die for use in asmart card, characterized in that: (a) the semiconductor die is lessthan 0.008 between 0.004 and 0.007inches thick; and (b) thesemiconductor die includes an active device equipped to operate at an RFfrequency greater than 20 Khz.
 3. A smart card including: (a) a memorydevice, and/or (b) a processing device, wherein the memory device andthe processing device are fabricated using a semiconductor die having athickness of 0.008 inches or less between 0.004 and 0.007 inches.
 4. Asmart card including: (a) a memory device, and/or (b) a processingdevice, wherein the memory device and the processing device arefabricated using a semiconductor die having a thickness of 0.008 inchesor less between 0.004 and 0.007 inches, and wherein the processingdevice operates at a speed greater than or equal to 4.0 Mhz.
 5. Asemiconductor die for use in a smart card package having a neutral planedefined as the plane of substantially zero mechanical strain duringmechanical flexure of the smart card package, characterized in that: (a)the semiconductor die is less than 0.008 between 0.004 and 0.007inchesthick, and (b) at least a portion of the semiconductor die is positionedwithin the neutral plane of the smart card package.
 6. A semiconductordie as set forth in claim 5 further including a plurality of diodes andtransistors defining an active surface within the semiconductor die, theactive surface being positioned within the neutral plane of the smartcard package.
 7. A semiconductor die as set forth in claim 5 furtherincluding a plurality of diodes and transistors defining an activesurface within the semiconductor die, the active surface beingpositioned within the neutral plane of the smart card package, and atleast one of the plurality of transistors adapted for operation at an RFfrequency greater than 20 KHz.